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It is common in film, literature and, currently, also in the world of video games; Homer Simpson travels through time using a broken toaster, The Doctor voyages through space and time to combat injustice across the universe and Marty McFly accidently goes back in time using an eccentric DeLorean. All these acclaimed movies and TV Shows have stories in which the plot unfolds through a temporal maze, where the protagonists are lost in the intricate fabric of space and time. Of course, there are plenty of other stories with much more convoluted and complicated plots. In the recent film, Coherence, for example, a group of friends travel across alternate realities only to get lost. We are accustomed to enjoy these stories in literature and film, but what does science says about all this?It was always thought that space and time were two universal concepts, i.e., time flows at the same speed throughout the universe, and that this space is one and the same for everyone. This idea, apparently common sense, was destroyed by the theory of special relativity that was presented by the ingenious Albert Einstein more than a century ago. According to this theory, space and time are unitary structure known as the space-time continuum.Since the inception of the space-time continuum, time travel has gradually sneaked in from the fiction to real science. Scientists are doing experiments that would allow them to travel through time since the 1960s. The first scientifically supported journey took place in October 1971. Back then two American physicists Joseph Hafele and Richard Keating flew their airliners once eastwards and once westward around the world. These airliners carried aboard four atomic cesium clocks. Upon their return, they compared the time of these clocks with that of a stationary clock in the US Naval Observatory at Washington, and lo and behold: the clocks didn’t corroborate with the immobile one. The time had passed quickly for the flying physicists who therefore went into the future – if only for about 60 nanoseconds.This brings us to the interesting concept of time dilation. Gravity as we know it exerts a force downwards on the position of a body in space. Applying gravity to the space-time continuum will lead to a ‘groove’ in time that corresponds to the force of the gravity. Looking at it practically, a much stronger time dilation would result when an astronaut flies at the speed of light to a distant star than that observed in the Hafele-Keating experiment. To demonstrate this effect, if the spaceman in question had a twin brother who remained on earth, then when he comes back there will be an evident age difference between the two (Interstellar anyone?). The brother who went into space will be younger than the one who remained on earth.Interestingly, time travel is not possible in the theoretical past. Overall, physicists have come to the consensus that if a trip is to be done in time, it would only be possible in the future, and that in the case of traveling into the past one could not travel to a date prior to the creation of the time machine. This statement would avoid thorny questions like why have we not yet been visited by travelers from the future? And that can someone travel to a time before he/she is born?

One of the interesting possible means of time travel is the wormhole, also known as the Einstein-Rosen bridge. A wormhole is a tunnel that acts as a shortcut between two different points in space-time. Its existence is predicted by the general theory of relativity through which its geometry is described as spheroidal at the two ends with a constricted ‘throat’ in between. It looks quite good on paper but there are a lot of factors that go against

Figure 2. A graphical depiction of a wormhole

wormholes’ use as time machines. First of all the force of gravity at its center would be immense and to overcome it, travelling at the speed of light is required which is theoretically impossible. Also, no primordial wormhole has been discovered yet. Apart from these drawbacks there are other hindrances that include: question about the hole’s own stability, quantum effects which would prevent the hole from keeping open and the intense, potentially lethal radiation emanated at the entrance of the hole.The answer may lie in engineering wormholes, with close to or less than 1g of gravity, ourselves. Of course, today it is impossible to create a hole like this. However, presently there is speculation about the possible creation of micro wormholes in particle accelerators, and about ways to stretch them to sizes that allow a human being to go through them. But these claims are nothing more than conjecture, and great physicists such as Stephen Hawking say that the turmoil arising from quantum uncertainty (known as vacuum fluctuation) would result in the wormhole collapsing in on itself at configurations fit for time travel. It is certainly too early to give a definitive answer to anything related to this matter, and as has always happened with science, gradually we find little clues that will open and close doors to countless amazing possibilities. Who knows, maybe there is a time travel surprise waiting for us in the future!!By Kevin F. Soul ScienceCheck Out This Video-4 Real Cases of Time Travel!